1. Field of the Invention
The present invention relates to an endoscope apparatus and in particular to an endoscope apparatus for performing color correction in accordance with driving time of a light source section.
2. Description of the Related Art
Conventionally, an endoscope apparatus comprises an endoscope having an image pickup device such as a CCD for picking up an image of a subject inside a living body, a light source integrated type processor including a light source such as an LED that supplies illumination light for illuminating the subject to the endoscope and a processor that converts an image pickup signal picked up by the CCD into a video signal and outputs the video signal, and a monitor that displays an image according to the video signal outputted from the light source integrated type processor.
Further, in recent years, a light source has been put into practice that forms illumination light of a desired color, using a light emitting source that emits excitation light and a fluorescent substance that emits fluorescence having a color (wavelength) different from a color of the excitation light by being exited by the excitation light, by combining the fluorescence from the fluorescent substance and excitation light that has transmitted through the fluorescent substance without being absorbed by the fluorescent substance, as a light source for supplying illumination light to a subject. For example, in Japanese Patent Laid-Open Publication No. 2011-67267, there is disclosed an endoscope apparatus which, by using a blue light laser source that emits blue laser light and a fluorescent substance that absorbs a part of energy of the blue laser light and emits green-yellow fluorescent light, forms white illumination light using green-yellow fluorescent light by the fluorescent substance and blue laser light that has transmitted through the fluorescent substance without being absorbed by the fluorescent substance.
In such an endoscope apparatus which forms illumination light of a desired color using the light emitting source that emits the excitation light and the fluorescent substance, a wavelength and emission strength of the excitation light emitted from the light emitting source changes in accordance with elapse of time from a start of use of the light emitting source to lose a color balance of the illumination light. Therefore, in the endoscope apparatus, a chromaticity correction table which is necessary for correction processing of adjusting an image signal to have a proper chromaticity is stored in advance and the color correction processing is performed with respect to the image signal based on correction data stored in the chromaticity correction table.
Incidentally, in such an endoscope, light adjustment for adjusting an amount of the illumination light is performed at the light source and is realized, for example, by the PWM (pulse width modulation) for performing variable control of a pulse width (driving time) which is a width of a pulse supplied to the light emitting source and during which the light emitting source is turned on while keeping a current value constant, or the variable current for performing variable control of a value of a current to be supplied to the light emitting source.
Further, there is an endoscope apparatus which performs the light adjustment using an electronic shutter of an image pickup device without performing the light adjustment at the light source, but a circuit scale of the image pickup device is increased if an electronic shutter function is equipped. In general, in the endoscope apparatus, it is necessary to downsize the image pickup device arranged at a distal end of an insertion portion in order to reduce a diameter of the insertion portion of the endoscope, and therefore an image pickup device not equipped with the electronic shutter function is used.